if CONFIG_NET_IPGRE is enabled, but CONFIG_IPV6 is disabled:

    net/ipv4/ip_gre.c: In function ‘ipgre_err’:
    net/ipv4/ip_gre.c:144:22: error: variable ‘data_len’ set but not used [-Werror=unused-but-set-variable]
      144 |         unsigned int data_len = 0;
	  |                      ^~~~~~~~

Fix this by moving all data_len processing inside the IPV6-only section
that uses its result.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202501121007.2GofXmh5-lkp@intel.com/
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
v2:
  - Do not use the ternary operator,
  - Target net-next.
---
 net/ipv4/ip_gre.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index f1f31ebfc7934467..9667f27740258efb 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -141,7 +141,6 @@ static int ipgre_err(struct sk_buff *skb, u32 info,
 	const struct iphdr *iph;
 	const int type = icmp_hdr(skb)->type;
 	const int code = icmp_hdr(skb)->code;
-	unsigned int data_len = 0;
 	struct ip_tunnel *t;
 
 	if (tpi->proto == htons(ETH_P_TEB))
@@ -182,7 +181,6 @@ static int ipgre_err(struct sk_buff *skb, u32 info,
 	case ICMP_TIME_EXCEEDED:
 		if (code != ICMP_EXC_TTL)
 			return 0;
-		data_len = icmp_hdr(skb)->un.reserved[1] * 4; /* RFC 4884 4.1 */
 		break;
 
 	case ICMP_REDIRECT:
@@ -190,10 +188,16 @@ static int ipgre_err(struct sk_buff *skb, u32 info,
 	}
 
 #if IS_ENABLED(CONFIG_IPV6)
-	if (tpi->proto == htons(ETH_P_IPV6) &&
-	    !ip6_err_gen_icmpv6_unreach(skb, iph->ihl * 4 + tpi->hdr_len,
-					type, data_len))
-		return 0;
+	if (tpi->proto == htons(ETH_P_IPV6)) {
+		unsigned int data_len = 0;
+
+		if (type == ICMP_TIME_EXCEEDED)
+			data_len = icmp_hdr(skb)->un.reserved[1] * 4; /* RFC 4884 4.1 */
+
+		if (!ip6_err_gen_icmpv6_unreach(skb, iph->ihl * 4 + tpi->hdr_len,
+						type, data_len))
+			return 0;
+	}
 #endif
 
 	if (t->parms.iph.daddr == 0 ||
-- 
2.43.0

On 1/20/25 2:12 PM, Geert Uytterhoeven wrote:
> if CONFIG_NET_IPGRE is enabled, but CONFIG_IPV6 is disabled:
> 
>     net/ipv4/ip_gre.c: In function ‘ipgre_err’:
>     net/ipv4/ip_gre.c:144:22: error: variable ‘data_len’ set but not used [-Werror=unused-but-set-variable]
>       144 |         unsigned int data_len = 0;
> 	  |                      ^~~~~~~~
> 
> Fix this by moving all data_len processing inside the IPV6-only section
> that uses its result.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202501121007.2GofXmh5-lkp@intel.com/
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

## Form letter - net-next-closed

The merge window for v6.14 has begun. Therefore net-next is closed
for new drivers, features, code refactoring and optimizations.
We are currently accepting bug fixes only.

Please repost when net-next reopens after Feb 3rd.

RFC patches sent for review only are obviously welcome at any time.

See:
https://www.kernel.org/doc/html/next/process/maintainer-netdev.html#development-cycle
---
Note: this is possibly somewhat borderline, but I prefer to avoid
exceptions unless there is something really ... exceptional ;)

/P

On Mon, Jan 20, 2025 at 02:12:36PM +0100, Geert Uytterhoeven wrote:
> if CONFIG_NET_IPGRE is enabled, but CONFIG_IPV6 is disabled:
> 
>     net/ipv4/ip_gre.c: In function ‘ipgre_err’:
>     net/ipv4/ip_gre.c:144:22: error: variable ‘data_len’ set but not used [-Werror=unused-but-set-variable]
>       144 |         unsigned int data_len = 0;
> 	  |                      ^~~~~~~~
> 
> Fix this by moving all data_len processing inside the IPV6-only section
> that uses its result.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202501121007.2GofXmh5-lkp@intel.com/
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
> v2:
>   - Do not use the ternary operator,
>   - Target net-next.

Thanks Geert,

This has been bothering me too.

Reviewed-by: Simon Horman <horms@kernel.org>